Injection Molding Precautions

- Feb 27, 2018-

Precautions Injection molding is an engineering technique that involves transforming plastic into a useful product that retains its original properties. The important process conditions for injection molding are the temperature, pressure and the corresponding individual action times that influence the plasticizing flow and cooling. Fold temperature control 1, cylinder temperature: injection molding process need to control the temperature of the cylinder temperature, nozzle temperature and mold temperature. The temperature of the first two passes mainly affects the plasticization and flow of the plastic, and the latter one mainly affects the flow and cooling of the plastic. Each plastic has a different flow temperature, the same plastic, due to different sources or grades, the flow temperature and decomposition temperature is different, which is due to the average molecular weight and molecular weight distribution due to different types of plastic injection Machine plasticizing process is different, so choose the barrel temperature is not the same.

2, the nozzle temperature: the nozzle temperature is usually slightly lower than the cylinder maximum temperature, which is to prevent the melt in the through-nozzle may occur "salivation phenomenon." The temperature of the nozzle should not be too low, otherwise it will cause the premature coagulation of the melt to block the nozzle or affect the performance of the product due to the early coagulation injected into the cavity.

3, mold temperature: mold temperature on the intrinsic properties of the product and the apparent quality of a great influence. Mold temperature depends on the level of crystallinity of plastic, the size and structure of the product, performance requirements, as well as other process conditions (melt temperature, injection speed and injection pressure, molding cycle, etc.).

Pressure control The pressure during the injection molding process includes plasticizing pressure and injection pressure, both of which directly affect plasticization of plastic and product quality. 1, plasticization pressure: (back pressure) When using the screw injection machine, the pressure at the top of the screw melt back in the screw rotation is called the plasticization pressure, also known as back pressure. The size of this pressure can be adjusted by the pressure relief valve in the hydraulic system. In the injection, the plasticizing pressure is the same size with the screw speed, then increase the plasticizing pressure will increase the melt temperature, but will reduce the plasticization speed. In addition, increasing the plasticizing pressure can make the temperature of the melt uniform, mix the pigment evenly and discharge the gas in the melt. In general operation, the pressure of plasticizing should be as low as possible while ensuring the quality of the product. The specific value varies with the type of plastic used, but rarely exceeds 20㎏ / c㎡.

2, injection pressure: In the current production, almost all of the injection machine injection pressure is based on the top of the plunger or screw on the pressure exerted by the plastic (by the oil pressure conversion) shall prevail. Injection pressure plays a role in injection molding by overcoming the resistance of the plastic from flowing from the cylinder to the cavity, by the rate at which it is charged, and by compaction of the melt.      Injection pressure Dividing rubber pressure and holding pressure, usually 1 to 4 injection pressure +1 to 3 pressure holding pressure, the pressure is generally less than the injection pressure, according to the actual use of plastic materials to achieve good Physical properties, appearance and size requirements.